Outgoing Homeland Security Secretary Janet Napolitano on Tuesday defended her decision to allow so-called Dreamers a chance to obtain legal status to stay in the United States and blamed Congress for failing to act on immigration reform.

Napolitano, who is leaving the Obama administration Sept. 6 to become chancellor of the University of California system, pointed the finger at Congress for failing to pass the DREAM Act to provide a path to citizenship for children brought to the country illegally by their parents.

“We instructed our immigration agents and officers to use their discretion under current law to not pursue low-priority immigration cases, like children brought to the United States illegally by their parents,” she said at a National Press Club speech. “Congress had a chance to give these so-called Dreamers a way to stay in our country through the DREAM Act, but unfortunately, that legislation failed to garner the 60 votes needed for cloture, falling just five votes short, despite strong bipartisan support.”

Napolitano said she used her “prosecutorial discretion” to allow Dreamers to obtain legal status to stay in the country and said more than 80 percent of the 500,000 requests for deferred action have been approved in the program’s first year.

The deferred action program, Napolitano said, “is no substitute for comprehensive immigration reform, which is the only way to fix the longstanding problems with our immigration system.”

Napolitano gave equal weight to the administration’s enforcement and deportation measures as she did to efforts to create paths to legal status for undocumented immigrants.

DHS has “invested historic resources to prevent illegal cross-border activity” that she said has caused illegal border crossings to drop to “near 40-year lows.”

“We also set common-sense immigration enforcement priorities, with a focus on criminals, national security and public safety threats, repeat offenders and egregious immigration violators,” she said. “Last year,

Napolitano also addressed one of her lowest moments as secretary — when she declared “the system worked” after the 2009 Christmas Day bomber managed to board a Detroit-bound plane from Amsterdam with a bomb. She did not mention her much-maligned words responding to the incident.

“From that attempted attack, we learned that relevant information possessed by U.S. Customs and Border Protection needed to be available overseas — at the last point of departure for the U.S. We fixed that,” she said. “We learned that our adversaries were moving to non-metallic devices. We adapted our screening technology and tactics to counter that.

“And we learned that a single vulnerability in any part of the aviation system can make everyone connected to it vulnerable,” she added. “Since we don’t control security in foreign airports, we have to work even more closely with international partners to raise the overall security of the system. We did that.”

She also praised the DHS efforts after Hurricanes Sandy and Irene and tornadoes in Missouri, Oklahoma and Alabama. And in doing so, she took a parting shot at the Bush administration’s bumbled response to Hurricane Katrina.

“As with our counterterrorism efforts, we drew important lessons from each of these events. Most notably, we built upon the lessons of Hurricane Katrina to put us in the best possible position to support the response to a major hurricane and make sure that response would be fast, flexible and comprehensive,” she said.

In what she called an “open letter” to her successor, Napolitano said it will be important for the next secretary — “him or her” — to prepare for simultaneous natural disasters “as a result of climate change.”

“You also will have to prepare for the increasing likelihood of more weather-related events of a more severe nature as a result of climate change, and continue to build the capacity to respond to potential disasters in far-flung regions of the country occurring at the same time,” she said.